Physics 24: The Big Bang, Week 3: Hubble s Law David Schlegel, LBNL

Transcription

1 Physics 24: The Big Bang, Week 3: Hubble s Law David Schlegel, LBNL 1905: Albert Einstein s theory of special relativity 1915: Albert Einstein s theory of general relativity 1920: Harlow Shapley & Heber Curtis debate over the size of the universe Shapley argues for a small Universe the size of the Milky Curtis argues for a big Universe, where other nebulae are island Universes 1920s: Edwin Hubble uses bright stars as standard candles Observations at Mt. Wilson in California Big Universe confirmed The Milky Way This image is mosaic of multiple shots on large-format film. It comprises all 360 degrees of the galaxy from our vantage. Photography was done in Ft. Davis, Texas for the Northern hemisphere shots and from Broken Hill, New South Wales, Australia, for the southern portions. Note the dust lanes, which obscure our view of some features beyond them. Infrared imaging reaches into these regions, and radio astronomy can look all the way through with less detail. The very center, however, shows a window to the farther side. In the center, stars are mostly very old and this causes the more yellow color. The final file is 1.5GB, and resolves details of less than one arcminute. Faintest stars are magnitude 11. (

2 This gas emits in OIII, Hα (green). The dust absorbs+scatters optical photons, re-radiating this energy in the far-infrared.

3 Sloan Digital Sky Survey - map of the sky

4 HST image of another island Universe, NGC 1365 (we now call these galaxies )

5 Physics 24: The Big Bang, Week 3: Hubble s Law Meanwhile , 1927: Alexander Friedman and Georges Lemaitre find solutions to Einstein s equations The general solutions are not static, but are expanding or contracting. Einstein introduces a cosmological constant (negative pressure term) to counteract the attractive force of gravity static solution (but unstable!) Solution for an empty Universe Big Bang Big Crunch

6 1929: Edwin Hubble publishes distance-redshift plot Distances from bright star standard candles (Cepheid variables) Redshifts (velocities) from Vesto Slipher s measurements Scatter interpreted as peculiar velocities from gravity of other galaxies Einstein abandons work on the cosmological constant, calling it his greatest blunder. Einstein visits Mt. Wilson in 1931 to thank Hubble.

7 Hubble s Law: v = H0 d Any two points move away from each other with a speed proportional to their distance s: Debate of Big Bang vs. Steady State Universe Obler s Paradox: If the Universe were infinite, static, and filled with a uniform distribution of stars, then every line of sight would end on a star. The sky would be as bright as the surface of a star. Question: How do we have an expanding Universe that appears unchanging? Matter creation?

8 What is a redshift? Galaxy at rest Galaxy receding at 16% speed of light

9 (Sordid) History of the Hubble constant (Hey... it s hard to measure a distance)

10 Sloan Digital Sky Survey (SDSS) Largest survey to date in area + volume Completed 10,000 deg 2 imaging in 5 colors (ugriz-bands) from drift-scanning Follow-up spectroscopy of 800,000 main galaxies to z~ ,000 luminous red galaxies to z~0.4 60,000 QSOs to z~4 Key project : Large scale structure + cosmology Timeline: : SDSS-I, completed : SDSS-II, in progress: legacy survey, supernova search, Milky Way Feb 2006: ARC call for white papers, two BAO white papers Jul 31, 2006: ARC call for proposals; APO LSS and 6 others submitted Nov 13, 2006: ARC board selects proposals : All dark/grey time for SSS (Milky Way) : All dark/grey time for APO LSS The SDSS 2.5-m Telescope Apache Pt., NM David Schlegel, Granada SIDE meeting 20 Jan 2007

11 Sloan Digital Sky Survey: 3D map

12 Discovery of Dark Energy ca Type Ia Supernovae Relative brightness fainter magnitude Perlmutter, Physics Today (2003) Supernova Cosmology Project High-Z Supernova Search Calan/Tololo Supernova Survey Accelerating Universe with vacuum energy without vacuum energy 0 empty mass density 1 21 Decelerating Universe redshift Scale of the Universe [relative to today's scale]

13 HST Cluster SN SNLS SN factory CMB David Schlegel, Granada SIDE meeting 20 Jan 2007

14 SNAP CMB David Schlegel, Granada SIDE meeting 20 Jan 2007

15 SNAP Baryon Osc. CMB David Schlegel, Granada SIDE meeting 20 Jan 2007

16 Acoustic Oscillations on the surface of last scattering (CMB)...and today in galaxy distribution 150 Mpc Today Supernovae standard candles Baryon oscillations standard rulers David Schlegel, Granada SIDE meeting 20 Jan 2007